1. Field of the Invention
The present invention relates to an improved anaerobic fermentation process for converting an influent liquid containing suspended organic matter to effluent gas and liquid products.
2. Description of the Prior Art
By-product or liquid waste streams containing suspended organic matter have heretofore been anaerobicly fermented to produce a methane-containing gas and other desired products. For example, waste water effluents from food processing plants commonly contain suspended organic matter, have high oxygen demands and are not acceptable under environmental laws and regulations for disposition in lakes or rivers. Such waste water streams are often processed in anaerobic and/or aerobic fermentation systems to remove the organic constituents and purify the waste water to an environmentally acceptable level.
In a typical anaerobic fermentation process, influent liquid containing suspended organic matter is introduced into an anaerobic fermentation zone which excludes air or oxygen and contains anaerobic microorganisms for converting the suspended organic matter to fermentation products. The fermentation products are comprised of a gas containing carbon dioxide and methane which is separated and utilized as an energy or heat source, and depending upon the particular type of influent liquid and organic matter contained therein, other products such as alcohols, antibiotics and the like can be produced. The anaerobic fermentation reaction produces bacterial cell mass, commonly referred to as sludge, which is recirculated to the reactor vessel. The effluent liquid produced is substantially free of organic matter and suspended solids.
The separation and removal of gas and bacterial cell mass from the reacted liquid have heretofore been accomplished by separate degasification and solids settling steps. That is, the reacted liquid containing suspended bacterial cell mass particles is conducted from the anaerobic fermentation reactor to a settling tank wherein the bacterial cell mass particles are allowed to settle to the bottom of the tank. The settled particles are withdrawn from the tank and recycled to the reactor. Gas entrained in the reacted liquid makes the suspended bacterial cell mass particles difficult to settle. Therefore, a degasifier is generally employed between the reactor vessel and the settling tank.
By the present invention an improved anaerobic fermentation process and apparatus are provided which eliminate the degasification and settling steps and substitute a flotation step which more economically and efficiently accomplishes degasification and separation of bacterial cell mass particles.